1. Field of the Invention
The present invention relates to a method of producing can bodies of a non-circular cross-section from planar of which the oppositely located edges of the blank will be interconnected in a longitudinal seam. The invention relates further to an apparatus for practicing said method.
2. Description of the Prior Art
Resistance roll-welding machines for the production of can bodies from planar blanks which include in addition to the welding device a bending apparatus for deforming the blanks and allow a production of a high number of can bodies per minute are generally known; these known machines are, however, suitable only for the production of cylindrical can bodies. Cans of non-circular cross-section, specifically such of a rectangular cross-section for receipt of foodstuff which are available on the market in high numbers have until now been produced predominantly by means of a soldering procedure during which the can bodies which have been shaped from planar blankets are conveyed through a soldering bath. The soldering material consists, however, to the largest part of lead and should therefore not come into contact with foodstuff, such that due to the presently increased attention given to the environment to be less burdened by noxious material there is the desire to substitute a different production method for the soldering method practiced for the production of cans. Cans are for instance generally known which have been produced by a soldering method and which have a rectangular cross-section and which taper towards their top and which due to this shape have the consumer recognizing that a specific content, such as a specifically prepared beef, is contained therein. This can having the function of a trade-mark shall quite obviously be maintained but at the same token it is desired to do away with the soldering method which until now has not been possible. Such cans are in many instances provided further with a tear-open strip extending therearound and defined by pre-scored scoring lines and including a tear-open flap located at one and such to allow an easy opening of the can without having to use a specific tool. This tear-open flap projects from one edge of the planar blank from which the can is produced, and due to this tear-open flap the production of such a can is made difficult still more if it cannot be produced by aid of the known soldering method.
In order to produce cans of a rectangular cross-section a compromise has already been made in that initially cylindrical cans were produced by the known resistance seam-welding method and thereafter deformed to a non-circular cross-section. If it is desired, however, to produce in addition to such rectangular shape a can which tapers towards one end by such method it is not possible to do such without a severe straining of the sheet metal due to the stretching or expanding of the sheet metal at the end having the larger cross-section. It is possible that the material ruptures and during the expanding of such a can body considerable stresses are generated therein which can lead to a bursting of the pre-scored lines. Such a production method is hardly advantageous and apart from such method there is quite a large necessity of machinery and correspondingly high investment costs therefore.
The blanks used for producing cylindrical can bodies are exactly rectangular whereas the blanks needed for a tapering can body must have a development of a truncated cone in which two opposite edges extend curvilinearly. The shape of the blank for a can body having a rectangular cross-section and rounded corners and in which additionally the size or magnitude of the cross-section changes continuously along the length of the can, i.e. in which a taper is present, is similar to above described development of the jacket of a truncated cone, but including rectilinearly extending partial sections at both outer edges. Such a blank leads after its deforming to a can body without any inner tensions and it is possible to conclude from the difference between the shapes of the blanks without any further ado that a can body which initially has been produced cylindrially can thereafter be forced only by a large expenditure of force into a rectangular and additionally tapering shape.